This invention relates to a toner for use in electrophotography as developer and more articularly to a method of producing such a toner.
The toner which is used as developer in electrophotography is usually a kneaded mixture of a resin material, a charge controlling agent and a colorant such as an organic pigment and is adapted to become electrostatically charged by friction with a carrier including reduced iron powder. Since colorants of many types are now available, toners can be of different colors such as red and blue and images of different colors can be formed therewith. Since toner particles become charged mainly through the charge controlling agent on their surfaces, their electrostatic characteristics are influenced significantly by the composition of the colorant present on their surfaces. Thus, if a toner of a different color is used, the composition of its colorant changes and hence also its electrostatic characteristics. As a result, it may happen that toner particles fail to become attached to a photosensitive surface effectively in an electrophotographic process and that the quality of the toner image formed thereon is adversely affected with the appearance of fog. In order to prevent such a result and to make the electrostatic characteristics of toner particles uniform, the types and quantities of charge controlling agents must be appropriately regulated by a very troublesome procedure. If different toners with different colorants are produced by using the same apparatus, on the other hand, different colorants and toner particles may become mixed together and sections with different electrostatic characteristics may appear locally. In order to prevent such an occurance, a washing machine may have to be provided for completely cleaning the production apparatus or a different production apparatus must be provided for toners with different colorants. By either method, production cost of toners becomes unreasonably high.